1. Field of the Invention
The invention relates to a device for expanding the dynamic range of a broadband analog/digital converter.
2. Discussion of the Background
The use of broadband analog/digital converters has made possible the development of modern broadband communication methods. However, the demands on the dynamics of the analog/digital converter, for example, in the reception device, have also increased together with the bandwidth of the communications method. The prior art resolves the dynamics problem by means of a pre-amplifier with a variable amplification factor and a downstream analog/digital converter. In this context, a regulating algorithm ensures a matched adjustment of the amplification factor, and, in this case, the actual level control is often derived from the digital sampled values.
However, a method of this kind is subject to a series of disadvantages. The variation of the analog amplification causes interference impulses. For amplitude-sensitive applications, the allocation of the digital signal sampled values for corresponding analog amplification is very important and can be realized only with great difficulty because of the variation of the analog amplification, if this is possible at all. Interference impulses lead to a short term overdrive of the analog/digital converter and, after the regulating procedure, lead to a reduction in sensitivity for an adjustable holding time. After every regulating procedure, the entire subsequent signal train, of the analog and also the digital part, must settle again, which, under some circumstances, leads to a significant reduction in the measurement rate.
The published international application no. WO 03/009478 A3 discloses an alternative dynamic expansion of analog/digital converters. An analog signal splitter splits the signal to be converted into N signal components. In every signal branch, an independent dither signal, which is subsequently removed again, is added to the signal, and the signal is then digitized by an analog/digital converter. The digital sampled values of every signal branch pass through an equalizer, which removes the errors in phase and amplitude. All channels are summated and equalized again. The disadvantage with this method is that, with every doubling of the number of analog/digital converters, exactly 3 dB of dynamic improvement is achieved. Accordingly, in order to achieve a dynamic improvement of 12 dB, 16 analog/digital converters are required. This is uneconomical and demands high precision in matching the many signal branches with one another. In the case of wide broadband applications, problems in the removal of the dither signal can occur in some circumstances, because a simple filtering is not possible in view of the broad bandwidth. The level of the dither signals must also be significantly higher than the level of the noise associated with the payload signal, because this noise is identical, that is to say, correlates on all channels. A calibration procedure is also required for the adjustment of the equalizers.
Therefore, there is a need for improved In order to resolve these problems of the prior art, therefore, there is a need for a simpler and more economical device for digitizing data, while providing a broad dynamic range, which generates only minimal or no interference through the dynamic expansion.